aquatic toxicity of airfield-pavement deicer materials and implications for airport runoff

Aquatic Toxicity of Airfield-PavementDeicer Materials and Implicationsfor Airport RunoffS T E V E N R . C O R S I , * , † S T E V E N W . G E I S , ‡

G E O R G E B O W M A N , ‡ G R E G G . F A I L E Y , §

A N D T R O Y D . R U T T E R †

U.S. Geological Survey Wisconsin Water Science Center,Middleton, Wisconsin 53562, Wisconsin State Laboratory ofHygiene, Madison, Wisconsin 53718, and General MitchellInternational Airport, Milwaukee, Wisconsin 53207

Received June 26, 2008. Revised manuscript receivedOctober 6, 2008. Accepted October 31, 2008.

Concentrations of airfield-pavement deicer materials (PDM)in a study of airport runoff often exceeded levels of concernregarding aquatic toxicity. Toxicity tests on Vibrio fischeri,Pimephales promelas, Ceriodaphnia dubia, and Pseudokirch-neriella subcapitata (commonly known as Selenastrumcapricornutum) were performed with potassium acetate (K-Ac) PDM, sodium formate (Na-For) PDM, and with freezing-point depressants (K-Ac and Na-For). Results indicate thattoxicity in PDM is driven by the freezing-point depressants inall tests except the Vibrio fisheri test for Na-For PDM which isinfluenced by an additive. Acute toxicity end points fordifferent organisms ranged from 298 to 6560 mg/L (as acetate)for K-Ac PDM and from 1780 to 4130 mg/L (as formate) for Na-For PDM. Chronic toxicity end points ranged from 19.9 to 336 mg/L(as acetate) for K-Ac PDM and from 584 to 1670 mg/L (asformate) for Na-For PDM. Sample results from outfalls at GeneralMitchell International Airport in Milwaukee, WI (GMIA)indicated that 40% of samples had concentrations greaterthan the aquatic-life benchmark for K-Ac PDM. K-Ac has replacedurea during the 1990s as the most widely used PDM atGMIA and in the United States. Results of ammonia samplesfrom airport outfalls during periods when urea-based PDM wasused at GMIA indicated that 41% of samples had concentrationsexceeding the U.S. Environmental Protection Agency (USEPA)1-h water-quality criterion. The USEPA 1-h water-quality criterionfor chloride was exceeded in 68% of samples collected inthe receiving stream, a result of road-salt runoff from urbaninfluence near the airport. Results demonstrate that PDM mustbe considered to comprehensively evaluate the impact ofchemical deicers on aquatic toxicity in water containing airportrunoff.

Introduction

During periods of freezing precipitation, airports must clearsnow and ice from runways, taxiways, and other pavedsurfaces to continue operations. Snow plows and rotary snowbrooms are used to remove loose snow and ice from

pavement, but when physical removal is not sufficient, theuse of chemical pavement deicing and anti-icing material(PDM) is necessary. The primary impact to aquatic systemsresulting from airport runoff containing PDM includespotential depressed oxygen due to elevated biochemicaloxygen demand (BOD) and aquatic toxicity (1, 2).

PDM consists primarily of freezing-point depressants(FPD) and water but also contains lesser concentrations ofvarious additives such as corrosion inhibitors and anticakingchemicals. Current FPDs used in liquid PDM includepotassium acetate- (K-Ac), potassium formate-, propyleneglycol-, and ethylene glycol-based fluids. FPDs used in solidPDM include sodium acetate and sodium formate (Na-For).Urea PDM formulations are available in liquid form mixedwith ethylene or propylene glycol and in solid (granular)form. In addition to chemical PDM, sand is used for addedsurface friction at many airports.

Direct application of liquid PDM helps to melt existingsnow and ice and reduce adhesion to pavement, therebyenhancing effectiveness of physical removal systems. Prewet-ting of pavement surfaces with liquid PDM is conducted inadvance of some freezing precipitation events to preventadhesion to pavement, facilitating physical removal of snowand ice. Solid PDM is applied directly to penetrate existingice, followed by application of liquid PDM to reduce adhesionof ice to paved surfaces. In addition, ice and packed snowwarrant application of a mixture of sand and solid PDM toimprove traction. Application rates of these chemical deicersare recommended by PDM manufacturers, with the greatestapplication rates recommended at intersections and hightraffic areas. Exact application methods can vary dependingon the airport and environmental conditions. One commonlyused system to reduce total usage is to apply PDM across theentire width of runways but only down the center of taxiways.

Fate and transport of spent PDM around the airfield isaffected by such factors as management of deicer-contami-nated stormwater, plowing to snowbanks, wind drift, seepagethrough pavement joints, seepage into pervious areas,tracking by aircraft and ground-support vehicles, drainageinto receiving surface- and groundwater systems, andeventual degradation. Because PDM is applied across a largearea throughout airports, containment of PDM into a deicer-management system is difficult and costly. For this reason,many deicer-runoff-management systems in place at airportsfocus on aircraft deicing and anti-icing application areas.Although some applied PDM that is not collected throughrunoff management degrades near the point of application(3), the remainder is presumably discharged to soils, ground-water, and surface water systems near airports.

Field studies of airport deicer impact on aquatic systemshave primarily been focused on aircraft deicers rather thanPDM. The limited field data that are available on environ-mental impact of PDM has primarily focused on urea deicersbecause of the dominance of urea in this market before themid-1990s. Although urea is still used at many airports, itsusage has decreased while acetate- and formate-based PDMhave gained popularity. Environmental impact was a factorin this change due to the BOD of urea and aquatic toxicityof ammonia, a degradation product of urea (1).

Studies of urea-based PDM in airport runoff at twodifferent airports concluded that use of urea-based deicershad adverse impacts on receiving water. Researchers fromthe United Kingdom reported a mean concentration of 106mg/L ammonia in airport surface runoff during seven“freezing” sampling periods as a result of urea degradationwith resulting toxic effects on tested organisms in the

* Corresponding author phone: (608) 821-3835; fax: (608) 821-3817; email: [email protected].

† U.S. Geological Survey.‡ Wisconsin State Laboratory of Hygiene.§ General Mitchell International Airport.

Environ. Sci. Technol. 2009, 43, 40–46

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receiving stream (4). Concentrations of ammonia-nitrogenas high as 53.3 mg/L from breakdown of urea and BOD5

concentrations as high as 942 mg/L from urea and glycolswere reported in airport-runoff samples from an airport inwestern Pennsylvania (5). In receiving streams, ammonia-nitrogen concentrations were detected up to 5.62 mg/L, andBOD concentrations were detected up to 355 mg/L. Resultingconditions included dense biological growth on the stre-ambed due to stimulation by the organic-waste load fromdeicers and a stressed community of aquatic organisms thatwere dominated by pollution-tolerant species. In comparisonto USEPA water-quality criteria (6), the above-cited literatureindicates that ammonia toxicity could sometimes be ofconcern with regard to aquatic toxicity in runoff from airportswhere urea deicers are in use.

Information regarding measured levels of acetate- andformate-based deicers in airport runoff and subsequent fieldevaluation of environmental impact could not be found forreview. Water from airport-deicer-recovery storage facilitieswas sampled by USEPA in 1999 that included one samplingperiod at each of four individual airports. Samples werecollected from paved airport surfaces during deicing activitiesto be treated or recycled for glycol content (1). This samplingwas focused more toward ethylene glycol- and propyleneglycol-based aircraft deicing fluids than PDM; however,potassium was detected at up to approximately 60 mg/L inthese samples (1). Acute aquatic toxicity end points (EC50)for K-Ac have been reported for Daphnia similis between1050 and 1210 mg/L, and chronic effects of reducedreproduction in C. dubia were reported at 600 mg/L, whichwas the lowest concentration tested (7). The range of acuteand chronic end points for formulated K-Ac roadway deicerproducts from two previous studies ranged from less than25 mg/L for the three-brood C. dubia IC25 to 3535 mg/L forthe 96-h IC50 for Pseudokirchneriella subcapitata (referred toas Selenastrum capricornutum) (8, 9).

Other available PDM products such as glycol-based fluidsare known to have impacts on BOD, but it is not possible todistinguish glycol from these PDM materials from glycoloriginating from aircraft deicers in airport-runoff samples.Information regarding glycol-based PDM in airport runoffand field evaluation of environmental impact due to PDMas opposed to aircraft deicers could not be found for review.

Because a change in PDM used at airports occurred inthe mid-1990s and environmental impacts of PDM productscurrently used at airports have not been thoroughly evaluated,this study was undertaken to better understand the potentialtoxicity levels of PDM, to investigate the source of observedtoxicity, and to provide a comparison of toxicity benchmarkconcentrations to concentrations measured in airport runoff.

MethodsAirport Operations. PDM were applied as needed at GeneralMitchell International Airport (GMIA) in Milwaukee, WI, toclear airport surfaces of snow and ice on 79 ha of pavement,including 5390 m of runway and 22 ha of terminal ramparea. Urea PDM was applied at GMIA through the middle ofthe 1998-99 deicing season, at which time its use was phasedout and it was replaced by acetate- and formate-based PDM.K-Ac (liquid) and Na-For (solid) PDM are the two PDMs usedat GMIA since 1998. Although PDM usage at GMIA has nothistorically been tracked, deliveries of K-Ac PDM to thisairport for the 2005-06 season totaled 888 000 L and deliveriesfor the 2006-07 season totaled 788 000 L. Formulated K-Acand Na-For PDM samples were collected on site directly fromstorage at GMIA in March 2005. Potassium formate (99.5%)and sodium acetate (99.8%) standards were purchased fromFischer Scientific, Fair Lawn, NJ.

Surface-Water Sampling. Water samples were collectedat four sites near GMIA from 1996 through 2006. A 2.31-km2

headwaters region of Wilson Park Creek was sampled toprovide water quality data for this section of the stream,which primarily drains an urban area (residential andcommercial) in addition to a small portion of runway anda U.S. National Guard facility at GMIA (Figure 1). There ispotential for a small amount of airport (and deicer) runoffto reach the upstream reference site, but most deicer runoffenters Wilson Park Creek downstream from this site. Thetwo airport outfall sites that contribute flow to Wilson ParkCreek were sampled to characterize runoff from the airport.The primary outfall site (Figure 1) includes flow from theupstream site combined with flow from storm sewers thatdrain the terminal area as well as some taxiways and runways.The secondary outfall (Figure 1) drains a small area of theairport where most air-cargo activities take place. This outfallenters Holmes Ave. Creek, which subsequently enters WilsonPark Creek approximately 0.8 km downstream from theprimary outfall. The drainage area of the primary outfall is5.83 km2 (3.52 km2 within the airport), and the drainage areaof the secondary outfall is 0.08 km2. The fourth samplingsite, referred to as the “receiving stream site”, is 5.54 kmdownstream from the airport, and is used to characterizewater-quality effects in the receiving stream. The streambetween the airport and the monitoring site alternatesbetween a concrete-lined and an earthen channel bottom.The drainage area of Wilson Park Creek at this point is 14km2. Immediately beyond this site, the stream drains intothe Kinnickinnic River, which flows for 4.33 km to theKinnickinnic River Estuary and eventually to MilwaukeeHarbor. Average flow at the four monitoring locations fromDecember through March is 17 L/s at the upstream site, 62L/s at the primary outfall, 1.3 L/s at the secondary outfall,and 309 L/s at the receiving stream site.

Airport personnel were contacted to determine whensignificant deicing was occurring and, thus, when samplesshould be collected. Precipitation data were collected by theNational Weather Service on airport property. Surface-water-quality sampling was conducted during 49 cold-weatherperiods, including 15 dry-weather periods and 34 runoffperiods with freezing precipitation that required applicationof deicers. Urea-based PDM was in use during 30 of these49 sampling periods, and acetate- and formate-based PDMwas in use for 19 of them. Dry-weather samples were collectedas grab samples by submerging the sample bottles directlyinto the water, immediately followed by appropriate pres-ervation through acidification or filtration. For samplingduring runoff periods, specific details of the sampling protocolused to collect and process water samples are outlined inCorsi et al. (10). Briefly, flow-weighted composite sampleswere collected at each site using refrigerated automaticsamplers and Teflon-lined polyethylene sample tubing(model 3700R, Isco Industries, Lincoln, NE). Samples weresubsequently split for separate chemical analyses, iced, anddelivered to the laboratory within 24 h. Constituents reportedin this paper include acetate, formate, and potassium.Constituents referenced in the Supporting Information forthis paper include sodium, ammonia-nitrogen, propyleneglycol, ethylene glycol, and chloride.

Stream-water level was measured every 5 min duringperiods of increased runoff and every hour during otherperiods using bubbler-type pressure transducers (SutronAccubar, Sutron Corporation, Sterling, VA). Flow was com-puted using a log-log relation between water level and flow(11).

Chemical Analysis. All chemical analyses were conductedat the Wisconsin State Laboratory of Hygiene. Acetate andformate were analyzed using methods as defined in themanual for the DIONEX AS15 separator column (DIONEX,Sunnyvale, CA). Instrument conditions are as follows: directinjection of 10 µL of water, use of a DIONEX AS15 separator

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column and AG15 guard column, gradient separation usingpotassium hydroxide eluent delivered using a DIONEX EG40eluent generator, and suppressed conductivity detectionusing electrolytic suppressor. Reporting levels were deter-mined as the concentrations below which spike recoveriesexceed 25% uncertainty (5 mg/L for acetate and 2.5 mg/L forformate).

Standardized methods used for analysis of potassium,sodium, propylene glycol, ammonia-nitrogen, and chlorideand resulting quality-control data for chemical analyses aresummarized in the Supporting Information (Table S1).

Toxicity Tests. Static renewal toxicity tests were conductedon formulated K-Ac- and Na-For-based PDM products andpure samples of the respective FPDs K-Ac and Na-For. Thesetests were conducted between March 2005 and September2006 for determination of acute- and chronic-end pointconcentrations. Test organisms used in acute tests includedthe marine bacterium Vibrio fischeri used in the Microtoxtest (15-min EC50), Pimephales promelas or fathead minnow(96-h LC50), and Ceriodaphnia dubia (48-h LC50). Test

organisms used in chronic tests included Pimephalespromelas (7-d IC25), Ceriodaphnia dubia (IC25), and the greenalga Pseudokirchneriella subcapitata (commonly known asSelenastrum capricornutum) (96-h IC25). Initial range-findingtests were conducted to approximate the appropriate toxicconcentration for each test organism. PDM concentrationsare reported as nominal (concentrations were calculated fromdilutions). All tests were conducted in accordance to standardUS EPA protocol (12, 13). Details of the toxicity-testingmethods have been previously reported (14) and are includedin the Supporting Information. Toxicity tests were conductedat the Wisconsin State Laboratory of Hygiene in Madison,Wisconsin.

Results and DiscussionToxicity of PDM Formulations and Freezing-Point Depres-sants. Test results indicate that toxicity end points forformulated K-Ac and Na-For PDM are similar to those of theFPD contained in the PDM (Table 1). This result indicatesthat toxicity of PDM is driven primarily by the acetate- and

FIGURE 1. Location of field study area and monitoring locations.

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formate- based FPDs rather than additives. The Microtoxtest result from the Na-For PDM is an exception to this patternbecause it resulted in a lower end point concentration fromthe formulated deicer than from the FPD. This result indicatesincreased sensitivity of the organism due to an additivecomponent, such as a corrosion inhibitor or anticaking agent,in the Na-For PDM. End point values in Table 1 are presentedas concentration of acetate or formate rather than concen-tration of the entire material tested to provide directcomparison to parameters monitored in airport runoff.Product literature indicates that the K-Ac-based PDM is 50%K-Ac, 50% water, and <1% corrosion inhibitor; the Na-For-based PDM is 98% Na-For with 2% additives.

P. promelas and C. dubia were more sensitive to K-Ac andthe K-Ac PDM than to Na-For and the Na-For PDM in acutetests. Microtox test results for the two FPDs showed greatersensitivity to K-Ac than to Na-For, but the opposite was truein formulated PDM, again indicating the influence of anadditive component in the Na-For PDM. All three organismsused in the chronic tests were more sensitive to K-Ac and theK-Ac PDM than to Na-For and the Na-For PDM.

In comparison to previous research conducted on glycol-based ADAF, the source of toxicity in the deicer formulationsis different. The most prevalent source of toxicity in PDMsis the FPD, whereas toxicity in ADAF is driven by proprietaryadditives such as corrosion inhibitors, surfactants, andthickeners (14, 15).

Pavement-Deicer Material in Airport Runoff. Monitoringof acetate- and formate-based PDM content in airport runoffwas conducted by analysis of the individual FPD ions whichinclude potassium, acetate, sodium, and formate. Potassium,acetate, and formate proved to be valuable indicators of PDMin runoff. Road salt (NaCl) dominated the sodium signal insamples, with chloride expressing a 1:1 molar relation tosodium in water samples (R2 ) 0.999); therefore, sodium wasnot useful in evaluation of airport PDM content. The relationof potassium to acetate concentrations shown in Figure 2illustrates a nearly 1:1 molar relation using data from bothoutfalls and the receiving stream, with the resulting slopefrom linear regression 3% less than the ratio of acetate topotassium molecular weights (acetate concentration ) 1.46× potassium concentration; R2 ) 0.95). However, residualsof this regression indicate a bias at concentrations ofpotassium less than 40 mg/L at all three sites, suggestingeither a background source of potassium other than PDMand/or some degree of acetate degradation before samplecollection.

Concentrations of acetate in the two airport outfalls rangedfrom less than 5 mg/L to 600 mg/L in 34 of 35 samples. The

concentration in the remaining sample was 3400 mg/L (Table2). Acetate concentrations in samples from the upstreamsite were all less than 6.5 mg/L. Samples from the receivingstream resulted in acetate concentrations of 78 mg/L or less.Concentrations of formate in the two airport outfalls rangedfrom less than 2.5 mg/L to 310 mg/L. Formate was notdetected in samples from the upstream site and was detectedin only one of 18 receiving stream samples at a concentrationof 12.5 mg/L.

The duration of sample-collection periods ranged frominstantaneous grab samples to composite samples up to 146 hlong, with a median sampling period of 17 h. Variability ofthese sampling-period durations is reflective of the variabilityin airport-deicer application and subsequent runoff periods.Intensive deicer-application periods can last anywhere fromseveral hours to several days, depending on the nature of theweather event that necessitates deicing activities. Subsequentrunoff periods are similarly variable in duration from severalhours to several weeks, dependent on the weather conditionsduring and after the deicer-application event. Deicer runoffduring periods of “wet” precipitation (rainfall, freezing rain,or snowfall during near- or above-freezing temperatures) ismore direct and shorter-term than during periods of snowfallwith subfreezing conditions and subsequent snowmeltperiods (16).

Toxicity Evaluation Using Aquatic-Life Benchmarks andWater-Quality Criteria. Toxicity units (TUs) have beencomputed as the ratio of the sample result to acute-toxicity-end point concentrations for K-Ac PDM and for Na-For PDMto facilitate evaluation of PDM toxicity (figure 3). Acute toxicityaquatic-life benchmarks for these PDMs were defined as the

TABLE 1. Toxicity-Test Results for Formulated Pavement Deicers and Freezing-Point Depressants (all units are expressed in mg/L)

acute-end point concentration(95% confidence interval)

chronic-end point concentraion(95% confidence interval)

test material Microtox (EC50) P. promelas (LC50) C. dubia (LC50) P. promelas (IC25) C. dubia (IC25) P. subcapitatad (IC25)

potassium acetate deicer(as acetate)a,b 6560 298 421 336 54.5 19.9

(3990-10800) (262-340) (355-499) (173-496) (41.3-121) (17.8-26.0)potassium acetate

(as acetate)a 6440 421 313 324 43.0 28.6

(5900-7220) (361-499) (259-379) (172-444) (30.8-78.9) (28.2-29.1)sodium formate deicer

(as formate)c 1780 4130 1860 1200 584 1670

(1450-2140) (3700-4620) (1600-2170) (856-1790) (506-707) (1390-1,820)sodium formate

(as formate) 23000 2300 1400 1190 713 2300

(22300-23600) (1980-2660) (1140-1730) (452-1330) (624-775) (2090-2490)a Multiply by 0.66 for toxicity end point expressed as potassium concentration. b Multiply by 3.32 for toxicity end point

expressed as original K-Ac deicer product. c Multiply by 1.54 for toxicity end point expressed as original Na-For deicerproduct. d Commonly known as Selenastrum capricornutum.

FIGURE 2. Comparison of acetate and potassium concentrationsin samples from monitoring sites receiving airfield-deicerrunoff.


concentrations associated with TU)0.5 for the most sensitiveof the three species tested (the lowest LC50 for each deicerin Table 1). A TU greater than 0.5 indicates that the sampleresult was greater than the aquatic-life benchmark, and aTU greater than 1.0 indicates that the sample result wasgreater than the LC50. This evaluation reflects techniquespreviously used by U.S. EPA and USGS in screening-levelecological risk assessments (http://www.epa.gov/oppefed1/ecorisk_ders/index.htm (17)).

Concentrations of acetate and formate in water samplescompared with end point concentrations for acute toxicityof PDMs indicate that runoff from PDM has potential toimpact aquatic toxicity at the outfalls and in the receivingstream site to a lesser degree. Potassium and acetate resultsfrom samples collected at the two airport outfalls indicatethat 40% of samples had concentrations greater than theacute aquatic-life benchmark, and 25% of these were greaterthan the LC50 for P. promelas (n ) 60). Formate results in

airport outfalls did not exceed the acute aquatic-life bench-mark for Na-For PDM in 35 airport outfall samples. Potassiumand acetate samples collected in the receiving stream indicatethat results for one of 32 samples collected exceeded theacute aquatic-life benchmark, and all sample resultswere less than the LC50 for P. promelas. Formate results fromthe receiving stream site were well below the acute aquatic-life benchmark for Na-For PDM.

An evaluation of data from November 1996 throughSeptember 1999, when urea PDM was in use at GMIA,indicates periodic elevated ammonia concentrations atairport outfalls (Supporting Information, Table A2). Airportoutfalls exceeded the 1-h USEPA water-quality criterion in41% of samples (n ) 109), including PDM application andnonapplication periods. Four-day average criteria werecompared with results from event-mean airport outfallsamples and low-flow grab samples, resulting in 13%exceedance (n ) 46). Samples from the upstream site andthe receiving stream site were all below the 1-h and 4-dayaverage water-quality criteria for ammonia.

Although this evaluation of toxicity is useful as a pre-liminary step in understanding the impact of PDM on surfacewater quality, results from K-Ac and Na-For PDM reportedhere are based on limited available toxicity data (acute endpoints from only three organisms) and exposure data fromonly one airport. A complete water-quality criterion evalu-ation for acetate- and formate-based PDM may well be morerestrictive than the acute aquatic-life benchmarks used here.Development of water-quality criterion would require theuse of toxicity data from more organisms and a broadergeographical consideration of exposure than is presentedfrom this study.

In addition, other contaminants that may affect toxicityare typically in airport runoff during the same periods whenPDM is present. Glycol-based ADAFs have potential to causetoxicity in airport runoff (18), as does road salt that is usedto clear snow and ice from paved surfaces outside of theairfield, such as parking lots and roadways (19). Glycol andchloride/sodium sample results provide an indication of thepresence of ADAF and road salt (Supporting Information,Table A2). Comparing these concentrations to toxicity-endpoint concentrations for ADAF and sodium chloride indicatesthat PDM was not the only influence on aquatic toxicity;ADAF and road salt would also influence toxicity in airportrunoff.

A recent study on toxicity of currently used ADAF productsreported acute- and chronic-toxicity end points of five type

TABLE 2. Summary of Constituent Concentrations in WaterSamples from Monitoring Sites Receiving Airport RunoffAssociated with Freezing-Point Depressants in PotassiumAcetate and Sodium Formate-Based Airfield-Pavement Deicers(all concentrations are reported in mg/L)

monitoring site

upstreamprimaryoutfall

secondaryoutfall

receivingstream

Acetate (2005-2007)10th percentile <5.0 9.8 16.5 5median <5.0 120 120 8.7590th percentile 6.44 404 535 29.7maximum 6.5 600 3,400 78no. of samples 17 19 16 18

Potassium (2000-2007)10th percentile 4.0 17.9 33.9 7.03median 6.25 59.1 112 15.590th percentile 11.0 338 1,140 38.1maximum 24.0 910 4,800 100no. of samples 32 34 26 32

Formate (2005-2007)10th percentile <2.5 <2.5 <2.5 <2.5median <2.5 11 14.5 <2.590th percentile <2.5 39.8 160 <2.5maximum <2.5 61 310 2.9no. of samples 17 19 16 18

FIGURE 3. Potassium acetate deicer toxicity units in airport-runoff samples with respect to the LC50 of Pimephales promelas (298 mg/L as acetate).


I formulations (deicers) and four type IV formulations (anti-icers) (14). Acute-toxicity end points for Vibrio fischeri,Pimephales promelas, and Ceriodaphnia dubia were reportedto range from 347 to 44 500 mg/L and chronic-toxicity endpoints of Pimephales promelas, Ceriodaphnia dubia, andPseudokirchneriella subcapitata (referred to as Selenastrumcapricornutum) were reported to range from 14.2 to 18 400mg/L. These toxicity end points vary widely because eachformulation has a unique set of additive components thatcontribute differently to overall toxicity. Because manydifferent ADAF products were used concurrently during thestudy period (at least four type I formulations and three typeIV formulations) and toxicity of each product is different, itis difficult to assess the relative influence of glycol-basedADAF compared to PDM. Many ethylene glycol and propyleneglycol concentrations in samples collected between Novem-ber 1996 and April 2007 at the two airport outfalls were withinthe range of these toxicity end points (Supporting Informa-tion, Table A2). By the time airport runoff reached thereceiving stream site, propylene glycol concentrations haddecreased more than 1 order of magnitude from those at theoutfalls, presumably due to dilution, dispersion, and deg-radation during transport through 5 km of stream channelfrom the airport.

Results of chloride and sodium analyses demonstratedthe influence of urban runoff in the Wilson Park Creekwatershed, especially downstream from GMIA. Concentra-tions of these road-salt-derived contaminants increased fromairport outfalls to the receiving stream because of salting ofroads, parking lots, and sidewalks downstream from airportdrainage. Between November 1996 and April 2007, 47 sampleswere collected for chloride at the receiving stream site, with68% of samples exceeding the hourly average USEPA water-quality criterion (860 mg/L) and 91% of samples exceedingthe 4-day average criterion (230 mg/L). Road-salt runoffappears to have a considerable effect on aquatic life in theWilson Park Creek watershed.

PDM, ADAF, and road salt combine to form a complexmixture of chemicals in airport runoff along with otherpotential contaminants commonly found in urban runoff. Ithas previously been recognized that ADAF, road salt, andurea PDM are of concern; however, acetate- and formate-based PDM have not been extensively evaluated in this regard.Sample results from the long-term monitoring program atGMIA have indicated that concentrations of ammonia-nitrogen (1996-1999) and potassium acetate (post 1999)resulting from PDM application within the airport were oftenpresent in outfalls at concentrations greater than aquatic-life benchmarks. Runoff from ADAF application was also apotential contributor to toxicity in airport runoff. In addition,road-salt runoff from urban areas surrounding the airportresulted in high chloride concentrations in the receivingstream, posing a substantial threat to aquatic life. Becausethis study was limited in scope to one airport, caution mustbe exercised in extrapolating conclusions to a broadergeographic region, but results from this study indicated thatconsideration of these airport-deicing products would benecessary for a comprehensive evaluation of the impact ofairport deicers on aquatic ecosystems.

AcknowledgmentsSupport for this research was provided by Milwaukee County(General Mitchell International Airport) and the U.S. Geo-logical Survey. We thank the biomonitoring, organic chem-istry, and inorganic chemistry units of the Wisconsin StateLaboratory of Hygiene for providing analytical services,especially Leroy Dobson and Amy Mager for analyticalcontributions. We thank many people in the U.S. GeologicalSurvey, Wisconsin Water Science Center, that contributed tothis research and Lisa Nowell for technical review of the

manuscript. Any use of trade, product, or firm names is fordescriptive purposes only and does not imply endorsementby the U.S. Government.

Supporting Information AvailableBioassay and chemical method details, quality assurancedata for chemical analyses presented in this report, anda table of sample results including ammonia, chloride,sodium, propylene glycol, and ethylene glycol. Thisinformation is available free of charge via the Internet athttp://pubs.acs.org.

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ES8017732


aquatic toxicity of airfield-pavement deicer materials and implications for airport runoff

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